Struts 2 in Action Struts 2 in Action DONALD BROWN CHAD MICHAEL DAVIS SCOTT STANLICK MANNING Greenwich (74° w. long.) For online information and ordering of this and other Manning books, please visit www.manning.com. The publisher offers discounts on this book when ordered in quantity. For more information, please contact: Special Sales Department Manning Publications Co. Sound View Court 3B fax: (609) 877-8256 Greenwich, CT 06830 email: [email protected] ©2008 by Manning Publications Co. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by means electronic, mechanical, photocopying, or otherwise, without prior written permission of the publisher. Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. 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Copyeditor: Benjamin Berg Sound View Court 3B Typesetter: Gordan Salinovic Greenwich, CT 06830 Cover designer: Leslie Haimes ISBN 1-933988-07-X Printed in the United States of America 12345678910–MAL –131211100908 To world peace and a global redistribution of prosperity brief contents PART 1STRUTS 2: A BRAND NEW FRAMEWORK ..................................1 1 ■ Struts 2: the modern web application framework 3 2 ■ Saying hello to Struts 2 20 PART 2CORE CONCEPTS: ACTIONS, INTERCEPTORS, AND TYPE CONVERSION ...................................................41 3 ■ Working with Struts 2 actions 43 4 ■ Adding workflow with interceptors 74 5 ■ Data transfer: OGNL and type conversion 101 PART 3BUILDING THE VIEW: TAGS AND RESULTS ...........................129 6 ■ Building a view: tags 131 7 ■ UI component tags 167 8 ■ Results in detail 202 vii PART 4IMPROVING YOUR APPLICATION .......................................229 9 ■ Integrating with Spring and Hibernate/JPA 231 10 ■ Exploring the validation framework 255 11 ■ Understanding internationalization 282 PART 5ADVANCED TOPICS AND BEST PRACTICES ............................307 12 ■ Extending Struts 2 with plug-ins 309 13 ■ Best practices 326 14 ■ Migration from Struts Classic 339 15 ■ Advanced topics 360 contents preface xvii acknowledgments xix about this book xxii about the title xxvii about the cover illustration xxviii PART 1STRUTS 2: A BRAND NEW FRAMEWORK ......................1 Struts 2: the modern web application framework 3 1 1.1 Web applications: a quick study 4 Using the Web to build applications 4 ■ Examining the technology stack 4 ■ Surveying the domain 8 1.2 Frameworks for web applications 9 What’s a framework? 10 ■ Why use a framework? 10 1.3 The Struts 2 framework 11 A brief history 11 ■ Struts 2 from 30,000 feet: the MVC pattern 12 ■ How Struts 2 works 15 1.4 Summary 18 ix x CONTENTS Saying hello to Struts 2 20 2 2.1 Declarative architecture 21 Two kinds of configuration 21 ■ Two mechanisms for declaring your architecture 22 ■ Intelligent defaults 25 2.2 A quick hello 25 Deploying the sample application 26 ■ Exploring the HelloWorld application 30 2.3 HelloWorld using annotations 36 2.4 Summary 38 PART 2CORE CONCEPTS: ACTIONS, INTERCEPTORS, AND TYPE CONVERSION .......................................41 Working with Struts 2 actions 43 3 3.1 Introducing Struts 2 actions 44 What does an action do? 44 3.2 Packaging your actions 46 The Struts 2 Portfolio application 47 ■ Organizing your packages 47 ■ Using the components of the struts-default package 50 3.3 Implementing actions 52 The optional Action interface 52 ■ The ActionSupport class 54 3.4 Transferring data onto objects 62 Object-backed JavaBeans properties 62 ■ ModelDriven actions 64 Last words on using domain objects for data transfer 67 3.5 File uploading: a case study 67 Getting built-in support via the struts-default package 67 ■ What does the fileUpload interceptor do? 68 ■ Looking at the Struts 2 Portfolio example code 69 3.6 Summary 72 Adding workflow with interceptors 74 4 4.1 Why intercept requests? 75 Cleaning up the MVC 75 ■ Reaping the benefits 77 Developing interceptors 78 4.2 Interceptors in action 78 The guy in charge: ActionInvocation 78 ■ How the interceptors fire 79 CONTENTS xi 4.3 Surveying the built-in Struts 2 interceptors 81 Utility interceptors 82 ■ Data transfer interceptors 82 Workflow interceptors 84 ■ Miscellaneous interceptors 88 Built-in stacks 90 4.4 Declaring interceptors 90 Declaring individual interceptors and interceptor stacks 90 Mapping interceptors to actions 93 ■ Setting and overriding parameters 94 4.5 Building your own interceptor 95 Implementing the Interceptor interface 95 ■ Building the AuthenticationInterceptor 95 4.6 Summary 99 Data transfer: OGNL and type conversion 101 5 5.1 Data transfer and type conversion: common tasks of the web application domain 102 5.2 OGNL and Struts 2 103 What OGNL does 103 ■ How OGNL fits into the framework 105 5.3 Built-in type converters 108 Out-of-the-box conversions 108 ■ Mapping form field names to properties with OGNL expressions 109 5.4 Customizing type conversion 122 Implementing a type converter 122 ■ Converting between Strings and Circles 123 ■ Configuring the framework to use our converter 124 5.5 Summary 126 PART 3BUILDING THE VIEW: TAGS AND RESULTS...............129 Building a view: tags 131 6 6.1 Getting started 132 The ActionContext and OGNL 132 ■ The ValueStack: a virtual object 135 6.2 An overview of Struts tags 137 The Struts 2 tag API syntax 138 ■ Using OGNL to set attributes on tags 139 xii CONTENTS 6.3 Data tags 142 The property tag 142 ■ The set tag 143 ■ The push tag 144 ■ The bean tag 145 ■ The action tag 148 6.4 Control tags 150 The iterator tag 150 ■ The if and else tags 151 6.5 Miscellaneous tags 152 The include tag 152 ■ The URL tag 153 ■ The i18n and text tags 154 ■ The param tag 156 6.6 Using JSTL and other native tags 156 6.7 A brief primer for the OGNL expression language 157 What is OGNL? 157 ■ Expression language features commonly used in Struts 2 157 ■ Advanced expression language features 163 6.8 Summary 165 UI component tags 167 7 7.1 Why we need UI component tags 168 More than just form elements 168 7.2 Tags, templates, and themes 174 Tags 175 ■ Templates 176 ■ Themes 176 7.3 UI Component tag reference 178 Common attributes 178 ■ Simple components 180 ■ Collection- backed components 190 ■ Bonus components 198 7.4 Summary 201 Results in detail 202 8 8.1 Life after the action 203 Beyond the page: how to use custom results to build Ajax applications with Struts 2 204 ■ Implementing a JSON result type 205 8.2 Commonly used result types 213 The RequestDispatcher, a.k.a. dispatcher 213 ■ The ServletRedirectResult, a.k.a. redirect 219 ■ The ServletActionRedirectResult, a.k.a. redirectAction 222 8.3 JSP alternatives 223 VelocityResult, a.k.a. velocity 224 ■ FreemarkerResult, a.k.a. freemarker 225 8.4 Global results 227 8.5 Summary 228 CONTENTS xiii PART 4IMPROVING YOUR APPLICATION...........................229 Integrating with Spring and Hibernate/JPA 231 9 9.1 Why use Spring with Struts 2? 232 What can dependency injection do for me? 232 ■ How Spring manages objects and injects dependencies 235 ■ Using interfaces to hide implementations 236 9.2 Adding Spring to Struts 2 238 Letting Spring manage the creation of actions, interceptors, and results 239 ■ Leveraging autowiring to inject dependencies into actions, interceptors, and results 242 9.3 Why use the Java Persistence API with Struts 2? 244 Setting your project up for JPA with Hibernate 245 ■ Coding Spring-managed JPA 249 9.4 Summary 253 Exploring the validation framework 255 10 10.1 Getting familiar with the validation framework 256 The validation framework architecture 256 ■ The validation framework in the Struts 2 workflow 258 10.2 Wiring your actions for validation 261 Declaring your validation metadata with ActionClass- validations.xml 262 ■ Surveying the built-in validators 265 10.3 Writing a custom validator 267 A custom validator to check password strength 267 ■ Using our custom validator 269 10.4 Validation framework advanced topics 271 Validating at the domain object level 271 ■ Using validation context to refine your validations 274 ■ Validation inheritance 277 ■ Short-circuiting validations 277 ■ Using annotations to declare your validations 278 10.5 Summary 280 Understanding internationalization 282 11 11.1 The Struts 2 framework and Java i18n 283 Retrieving localized text with ResourceBundle and Locale 284 ■ How Struts 2 can ease the pain of i18n 286 11.2 A Struts 2 i18n demo 287 A quick demo of Struts 2 i18n 287 ■ A quick look behind the scenes 290 xiv CONTENTS 11.3 Struts 2 i18n: the details 291 Struts 2 default TextProvider ResourceBundle location algorithm 291 Retrieving message texts from your bundles 295 ■ Using the i18n tag to specify a bundle 299 ■ Parameterizing your localized texts 299 ■ Formatting dates and numbers 301 11.4 Overriding the framework’s default locale determination 302 Letting the user interactively set the locale 302 ■ Programmatically setting the locale 305 11.5 Summary 305 PART 5ADVANCED TOPICS AND BEST PRACTICES ...............307